For alternators used in motor vehicles, such as trucks, railroads, etc. particular physical dimensions are associated with specific power outputs. A required power output must be met in consideration of the available space in the vehicle.
In alternators of a known type, the stator has slots which accommodate the three phases of a winding. The winding is so inserted into the slots that, electrically speaking, three different phases, each at an angle of 120.degree. to the others, result as a consequence of the magnetic induction of the rotating field generated by the rotor.
The rotating armature or rotor generally has an exciter winding to which a controlled current is applied and which rotates with the rotating armature. Alternatively, it is also stationary. In the latter case, an alternating magnetic field results from a particular shape of the armature (claw-pole rotor) which induces the voltages of correct phase in the stator windings. The stator windings can be connected in a .DELTA. connection or in a Y connection. If the exciter winding rotates with the armature, then the exciter current (DC current) is applied to it by two slip rings.
Since in motor vehicles a battery is generally used for energy storage, the circuits which constitute the load are DC circuits so that the AC current furnished by the alternator is rectified by means of bridge circuits before being applied to the load.
For winding the stator with the coils for generating the different phase voltages, two winding methods are known, namely wave winding and lap winding. The following discussion concerns itself mostly with the wave winding process. If three-phase generators are concerned, as is the case in motor vehicles, then the stator is wound with three coils, the rotation of the armature inducing a voltage in each of the coils which, as previously mentioned, is at a phase angle of 120 electrical degrees relative to the others.
The known wave winding method will now be explained with reference to FIGS. 1 and 3. The three coils to be wound in the wave winding are to be accommodated in the slots of the stator in such a way that the desired phase distribution results with a particularly high utilization factor for the space inside the slots. The method is illustrated schematically in FIG. 3. It is assumed that the stator unit is ring shaped and that the winding is to be inserted automatically into slots on the inner surface. The conventional stator has 36 slots, the number of slots presenting the best solution for the unit in view of the requirements for overall dimension, stability, and capacity for carrying the coils having particular wire thicknesses for carrying the required currents. In FIG. 3, slots 1-14 are pictured. Of course these will be continued by slots 15-35 (not shown); slot 36 then adjoins slot 1.
For a three-phase system, three coils I, II, and III are to be wound into the slots. The winding can begin with any selected coil, for example coil I, whose winding is inserted into slot 1, continues by an upper arc Ia into slot 4 and then through a lower arc Ib into slot 7, etc. It will be noted that a wave winding results, the straight portions of the coil being inserted into slots of the stator skipping two slots, until the required number of windings for the coil generating the voltage of the first phase has been manufactured. It will also be noted that winding of the stator with the first coil starting at slot 1 does not result in any difficulties. The windings or bars of the coil can be pushed down onto the bottom of the slot and nothing stands in the way of their insertion.
When coil II is to be considered, this situation is already different. First, only the mechanical winding procedure will be considered, the electrical connections being explained later on. The first bar or straight portion of coil II is to be inserted into slot 3. However, this part of coil II can already not be inserted properly to the bottom of the slot since at position x in the upper region of FIG. 3 a crossover occurs with the upper arc of coil I (shown in a solid line). This crossover cannot be avoided. This means that in this location the coil of phase winding II is pushed somewhat in the direction of the stator interior, that is does not sit properly in slot 3. Correspondingly, the upper arc IIa of winding II is somewhat slanted until insertion into slot 6. At slot 6, at least in the upper region thereof, this winding can be inserted without difficulty into the slot. However in the lower region, at y, a crossover again occurs with the already inserted and fully wound coil I. It will be noted that even the second coil II cannot be inserted without hindrance into the stator slots assigned thereto. This already decreases the utilization factor for the slots of winding II. However, the difficulty becomes extreme when coil III, illustrated in FIG. 3 in a dot dash line, is to be inserted. Even the schematic representation shown in FIG. 3 makes it clear that crossover points occur both at the top and at the bottom, that is at y' as well as at x' with the previously inserted arcs I.sub.a, I.sub.b, II.sub.a . . . of coils I and II. The crossovers take place very closely to the slot into which the third coil is to be inserted, starting with slot 5 and then following with slot 8, slot 11, etc. In other words, the previously inserted coils I and II prevent the straight portions or bars of coil III from being pushed to the bottom of their assigned slots. The slots for stators for which this winding method is utilized must therefore be relatively deep so that all windings of the three coils can be accommodated. Of course free space remains within the slots, since the previously wound windings are always in the way of windings to be inserted at a later time.
The situation is illustrated in perspective in FIG. 1. It will be noted that coil I is accommodated with ease in its associated slots, two slots always being skipped for a three-phase system. This is no longer the case even for coil II. At location x a crossover point of the upper arc IIa with the upper arc Ia occurs. At point 1, which is further away from crossover point x, the winding can still be inserted into the associated slot and pushed to the bottom thereof without interference.
However, it will be noted from the perspective view in FIG. 1, the third coil III cannot be inserted properly in any location, since both previously wound coils are in the way. Both upper and lower crossover points with winding II occur at x' and crossover points z (both on top) with winding I. The last winding III is thus wound only from the outside, that is from the interior of the stator, onto windings I and II, so that the space within the slots which is available for winding III is not fully utilized and cannot be fully utilized since the upper and lower arcs of the previously inserted coils prevent such utilization. The result of this known winding method is therefore not satisfactory insofar as obtaining an optimum utilization factor for the slot space is concerned. It must, of course, also be kept in mind that any winding method which results in full utilization of the space in the slots must also be suitable for automatic winding.